"Between the walks and not getting the out when he needed, that's what opens the floodgates [for the Brewers]," said Giants manager Bruce Bochy.
Estrada even got in on the act, ripping a two-run double down the left-field line for his first hit of the season and the first two RBIs of his career. But the right-hander pulled up rounding first and jogged slowly into second with a strained right hip flexor before limping off the field.
"I almost wish I would've struck out on that," Estrada said. "It's unfortunate, man. It's really bad timing right now that this happened."
The liner was hit right at Giants third baseman Joaquin Arias, and Estrada thought it had been caught, which caused him to pause for just a moment. But when he saw the ball move into the outfield, he pushed off to accelerate quickly, which is when he felt the injury.
"I felt a pop in my quad -- I kept hearing [it's] a hip flexor, but I felt a pop in my quad," said Estrada, who will undergo an MRI to determine the extent of the injury. "Hopefully, it's nothing serious."
If Estrada misses an extended period of time, he would be the second Brewers starter to go down this season. A season-ending injury to Chris Narveson's rotator cuff made Estrada the club's fifth starter a month ago.
Estrada's injury -- which came on a rare extra-base hit by the right-hander and which turned out to be the game's deciding hit -- is yet another tough break for the Brewers, who have also already lost Alex Gonzalez and Mat Gamel for the season with injuries.
"You try to get through these seasons and you know how important it is to keep everybody healthy," said manager Ron Roenicke, whose job gets more difficult with every injury. "We certainly haven't been able to do that."
And on a day when the Brewers needed a solid outing from their starter so as to ease the burden on their busy bullpen, Estrada was knocked out after just three batters.
Given a six-run lead, which increased to eight runs after a two-run homer in the second by Jonathan Lucroy, the Brewers' relievers struggled a bit before righting the ship over the last four frames.
But considering their recent workload, they delivered an impressive eight innings.
"The bullpen came in, did a great job," Lucroy said. "I know some guys have been throwing a lot lately, and they still did a great job, battled for us and kept us right in there."
Left-hander Manny Parra entered in place of Estrada, pitching for the fourth time in six games. After throwing a scoreless second inning, Parra gave up a three-run double in the third. Kameron Loe came on in the fourth and allowed a pair of runs on three hits and a walk in his fifth appearance in seven days.
Despite the five runs, Roenicke was happy with what he saw from Parra and Loe.
Another oft-used member of the 'pen, Jose Veras, came on in the sixth, also making his fifth appearance in the span of a week. Veras delivered a pair of clean innings to bridge the gap to Francisco Rodriguez and John Axford, who closed out the eighth and ninth, respectively.
Out of 61 total innings in the six games of the homestand, Brewers relievers pitched 28 1/3 of them, with the seven relievers combining to make 25 total appearances.
"Is that right? Yeah, that's a lot," Roenicke said. "The day off [on Thursday] is big."